DE 42 23 954 C1 describes a heating device for a drive unit in a motor vehicle. The heating device includes a heating element and at least one sensor. The sensor is designed in such a manner that it can detect a predetermined behavior of the vehicle user preceding the start of the drive unit. For example, the inserting of the buckle latch of a safety belt in the belt buckle may be detected. More precisely, the sensor detects the engaging of the buckle latch of the safety belt in the belt buckle. Here, the sensor interacts with a control device in such a manner that the control device switches on the heating element when the sensor detects the engaging of the buckle latch of the safety belt in the belt buckle.
Factually, the start of the drive unit by the vehicle user is mostly preceded by putting on a safety belt and the engaging of the buckle latch of the safety belt in the belt buckle accompanied by this, however the engaging of the buckle latch of the safety belt in the belt buckle cannot be understood as a secure indication that the start of the drive unit of the motor vehicle is imminent. It is rather conceivable that the vehicle driver initially puts on the safety belt so that the buckle latch of the safety belt engages in the belt buckle but following this waits for further vehicle users or passengers. Because of this a relatively long heating period is created so that the energy consumption of the heating element and the high loading of the battery of the motor vehicle through the heating element is increased. For this reason, DE 42 23 954 C1 also proposes additional sensors by means of which another predetermined behavior of the vehicle user preceding the start of the drive unit can be detected. In other words, for the sake of safety two or more sensors detect the respective predetermined behavior of the vehicle user before the heating element is switched on. This ultimately merely leads to a more complex construction of the heating device including its sensors.